Effects of maturity at harvest and cultivar on agronomic Effects of maturity at harvest and cultivar on agronomic performance of forage sorghum and the nutritive value of performance of forage sorghum and the nutritive value of selected sorghum silages selected sorghum silages

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Introduction
Several earlier studies on the effects of stage of maturity showed that harvesting forage sorghums at the late-dough stage optimized silage yields and nutritive values.
The objectives of this study were: 1) to document the effect of stage of maturity on agronomic performance over a wider range of forage sorghum phenotypes than was used in previous studies and 2) to continue to compare voluntary intake and DM digestibility of selected forage sorghum silages harvested in the late-dough stage.

Experimental Procedures
1990.Twenty forage sorghum cultivars were selected to represent a broad range of phenotypic characteristics and season lengths.All were grown under dryland conditions near the Kansas State University campus, Manhattan.
The 12-row plots were planted on June 4, and each cultivar was randomly assigned to three replications.Rows were 25 ft long with a 30inch spacing, and plots were thinned to uniform stands of 34,800 plants per acre.Cultivars were harvested at milk, late-dough, and hard-grain stages of kernel maturity.Agronomic data collected included days to half-bloom, plant height, lodging score, and whole-plant DM and grain yields.The first row in each plot was a border, and whole-plant DM yield for the first maturity stage was measured by harvesting the 2nd and 3rd rows with a precision chopper.All heads in the 4th row were clipped for grain yield determination.The plants in the 4th row were left standing to act as a border for the next harvest.

1989.
A voluntary intake and digestion trial was conducted with 12 grain and forage sorghum silages produced in 1989.The cultivars were grown under dryland conditions and harvested in the late-dough stage.Three mature wethers were assigned to each silage in the two-period trial.
The farm-scale plots were similar to those described last year (Rep. of Prog. 592;.However, dry soil conditions at planting on May 31 and subsequent very low rainfall until the second week in August (only 4.5 inches) produced thin and uneven stands, and one of the three replications for each cultivar was abandoned.Therefore, statistical analysis of the agronomic data shown in Table 4 is not reported, and the numerical values are presented for reference purposes only.

Results and Discussion
1990.Agronomic characteristics of the 20 forage sorghums are shown in Table 1.Blooming was delayed in all cultivars probably because of prolonged cool weather in the early part of the growing season.Time to half-bloom ranged from 64 to 83 days.Plant height varied greatly between cultivars and, as expected, the late-season hybrids were the tallest.
In the milk stage harvest, the only significant lodging occurred in three of the lateseason hybrids (i.e., DeKalb FS25E, Garst 333, and SeedTec Hi-Energy II).However, several other cultivars lodged with advancing maturity (i.e., Funk's 102F, Golden Acres T-E Silomaker, Oro Kandy Kane, NC + 940, Pioneer 843 and 947, and Rox Orange).A very high wind on August 30th caused the initial lodging, which appeared to be more severe for the higher grain-yielding hybrids.Plant height did not show a direct relationship to lodging; some of the shorter cultivars had high lodging scores (i.e., Funk's 102F, Silomaker, and Rox Orange), whereas several of the taller sorghums had very low lodging scores (i.e., Atlas, DeKalb FS5 and FS25E, NC+ NB305, and Pioneer 931).
The effects of cultivar and harvest stage on DM content and silage and grain yields of the 20 forage sorghums are presented in Tables 2 and  3. Very high rainfall (13.1 inches) from mid-July through August favored extended vegetative growth in the mid-and late-season hybrids, which resulted in higher whole-plant DM yields, particularly at the first two harvest stages, compared to the early-season sorghums.Limited rainfall during June and early-July resulted in relatively low whole-plant DM and grain yields for the early-season cultivars at the milk stage harvest (i.e., Buffalo Canex, Cargill 200F, Oro Kandy Kane, and Rox Orange).Whole-plant DM yields peaked at the late-dough stage; however, grain yields continued to increase and were highest at the hard-grain harvest.Eighteen of the 20 cultivars had their highest whole-plant DM yield at the late-dough stage and 14 of the 18 grain-producing sorghums had their highest grain yield at the hard-grain stage.The average harvest intervals were 12 days between the milk and late-dough and 13 days between the latedough and hard-grain stages.

Agronomic characteristics and results
of the voluntary intake and digestion trial are shown in Table 4. Dry matter intake was positively associated with DM digestibility, and the highest digestibilities were obtained for the high grain-yielding cultivars.Six of the 10 grain-producing forage sorghums had not reached the late-dough stage at the first frost on September 24.
The non-heading forage sorghum (Funk's G 1990) showed the lowest DM intake and digestibility, which is consistent with previous results for this cultivar.
1989 vs. 1990.Presented in Table 5 are minimum, maximum, and mean values for the agronomic characteristics of the 10 forage sorghum cultivars that were included in both the 1989 and 1990 late-dough stage harvests.Agronomic measurements were dramatically reduced in the 1989 growing season compared to 1990 (i.e., plant height and silage and grain yields).

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Cultivars that were between the late-dough and hard-grain stages at the first frost on Sept 24.**Hybrids that were in the mid-to-late milk stage at the first frost.***Hybrids that were in the early-milk stage at the first frost.

Table 5 . Minimum, Maximum, and Mean for the Agronomic Characteristics of 10 Forage Sorghum Cultivars Compared in Both 1989 and 1990
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